The tax bill also takes a swipe at gig worker classification, in addition to a provision that seeks to repeal the individual mandate to purchase health care coverage imposed by the Affordable Care Act. And in the midst of this hodgepodge of tax, employment and health law changes lurk language lifted from a prior House bill called the New Economy Works to Guarantee Independence and Growth Act, or NEW GIG Act.

According to the TaxProf Blog, that legislation, which the Congress' Joint Committee on Taxation last week suggested was added to the Senate draft of the tax bill, clarifies "worker classification" and income-reporting responsibilities in five major ways.

According to the report, it first "creates some tests easily met by any company hiring independent contractors that says these workers are not employees." It also says that anyone making more than $1,000 has to file a 1099 tax form reporting that income.

The third provision requires the company hiring the contractors to withhold 5 percent of the income paid—a new requirement, similar to full-time employers' obligations, but less than the current federal self-employment tax. Fourth, it limits the Internal Revenue Service from reclassifying contractors as employees. And fifth, it allows workers to sue in tax court.

"Our worry is that tax clarification of independent contractor status is a strategic step designed to win this broader (non-tax) regulatory war over worker classification," the blog says. "Our specific concern is that 'forced clarity' in tax can tilt the direction of the worker classification debate in a way desired by the platform businesses, industry lobbyists and the legislation's supporters."

But there's nothing in the law to limit such provisions to gig workers, say the authors. In fact, they argue that the law grants the legal presumption to employers that any worker management wants to treat as a contractor is designated as such under law, and by limiting the IRS's ability to reclassify contractors as employees, it shores up its pro-management position while at the same time absolving owners and management from many employer responsibilities for full-time employees, including the rights of workers to organize unions, earn minimum wages, outlaw child labor, and guarantee family and medical leave.

The report adds that the law also calls into question the applicability of anti-discrimination laws and health and safety regulations.

Forbes reports that the effect of the law "likely would be less steady work, greater tax impacts on workers, a loss of benefits including healthcare insurance, and elimination of many protections provided by labor law."

Not only that, says the Alternet report, "gig economy workers and contractors ought to be aware that the GOP Congress is considering legislation that would skim 5 percent off their earnings—to be withheld for federal taxes by their employers. That's in addition to contractors itemizing their expenses, which are deductible."

The blog authors write, "If one is going to sign off on this type of legislation, one should at least be aware of what the far-reaching consequences may be in order to make a conscious determination that it's still worth doing despite these wide-ranging non-tax risks and costs. Or, if one's underlying normative goal is to harness tax reform in order to dilute worker protections in pursuit of business growth, one should be transparent about that too."